OpenBSD-4.6/share/man/man4/hotplug.4

.\"	$OpenBSD: hotplug.4,v 1.3 2007/05/31 19:19:50 jmc Exp $
.\"
.\" Copyright (c) 2004 Alexander Yurchenko <grange@openbsd.org>
.\"
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.\" purpose with or without fee is hereby granted, provided that the above
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.Dd $Mdocdate: May 31 2007 $
.Dt HOTPLUG 4
.Os
.Sh NAME
.Nm hotplug
.Nd devices hot plugging
.Sh SYNOPSIS
.Cd "pseudo-device hotplug 1"
.Pp
.Fd #include <sys/types.h>
.Fd #include <sys/device.h>
.Fd #include <sys/hotplug.h>
.Sh DESCRIPTION
The
.Nm
pseudo-device passes device attachment and detachment events to
userland.
When a device attaches or detaches, the corresponding event is queued.
The events can then be obtained from the queue through the
.Xr read 2
call on the
.Pa /dev/hotplug
device file.
Once an event has been read, it's deleted from the queue.
The event queue has a limited size and if it's full all new events will be
dropped.
Each event is described with the following structure declared in the
.Aq Pa sys/hotplug.h
header file:
.Bd -literal -offset indent
struct hotplug_event {
	int		he_type;	/* event type		*/
	enum devclass	he_devclass;	/* device class		*/
	char		he_devname[16];	/* device name		*/
};

.Ed
The
.Va he_type
field describes the event type and can be either
.Dv HOTPLUG_DEVAT
for device attachment or
.Dv HOTPLUG_DEVDT
for detachment.
The
.Va he_devclass
field describes the device class.
All device classes can be found in the
.Aq Pa sys/device.h
header file:
.Bd -literal -offset indent
enum devclass {
	DV_DULL,	/* generic, no special info */
	DV_CPU,		/* CPU (carries resource utilization) */
	DV_DISK,	/* disk drive (label, etc) */
	DV_IFNET,	/* network interface */
	DV_TAPE,	/* tape device */
	DV_TTY		/* serial line interface */
};

.Ed
The
.Va he_devname
is a device name including unit number, e.g.\&
.Pa sd1 .
.Pp
Only one structure can be read per call.
If there are no events in the queue, the
.Xr read 2
call will block until an event appears.
.Sh DIAGNOSTICS
.Bl -diag
.It "hotplug: event lost, queue full"
New events will be dropped until all pending events have been read.
.El
.Sh SEE ALSO
.Xr read 2 ,
.Xr hotplugd 8
.Sh HISTORY
The
.Nm
device first appeared in
.Ox 3.6 .
.Sh AUTHORS
The
.Nm
driver was written by
.An Alexander Yurchenko Aq grange@openbsd.org .